Recently, there is a desire to develop superconductive magnets generating higher magnetic fields in response to the increasing demands for high magnetic field magnets in such fields as nuclear fusion, high energy physics research and solid state physics research. The wire rods for superconductive magnet put into practical use up to the present have been Nb-Ti alloy base wire rods and Nb.sub.3 Sn and V.sub.3 Ga compound base wire rods, but since their critical magnetic fields are said to be about 11T (tesla) and 22T at 4.2 K. respectively, the maximum magnetic field obtained as a superconductive magnet would be about 14T in due regards to current capacity and efficienty. If it is desired to achieve an even higher magnetic field, raw materials of a higher level critical magnetic field would be necessary.
From such a technical background, the compounds called "Chevrel-phase compounds" which are Mo ternary calcogenide, have been drawing attention, and among them the Chevrel-Phase lead molybdenum sulfide PbMo.sub.6 S.sub.8 (PbMo.sub.6 S.sub.8 herein after) has been highly evaluated due to its high critical magnetic field reaching over 50T at 4.2 K. so that it can be said that a critical magnetic field of around 20-30T could possibly be generated if a magnet employing this compound is put into practical use.
Concerning PbMo.sub.6 S.sub.8, recent improvements in the fabrication of PbMo.sub.6 S.sub.8 wires by a powder-metallurgical-technique have been described in IEEE Transaction on Magnetics, Vol. Mag-19, No. 3 May 1983, P402-405, "Investigation of the Properties of PbMo.sub.6 S.sub.8 Powder Processed Wires", on the synthesis of PbMo.sub.6 S.sub.8 by employing an Ag barrier in the Journal of Applied Physics 49 (2) February, 1978, P936-938, "Superconducting Wires of PbMo.sub.5.1 S.sub.6 by a Power Technique", on the study of a process for producing PbMo.sub.6 S.sub.8 compound wire rod material by power-metallurgical-techniques using Mo barrier in "Ternary Superconductors" published 1981 by Elsevier North Holland, Inc. Shenoy, Dunlap, Fradin, eds., "PbMo.sub.6 S.sub.8 : A new Generation of Superconducting Wires?", respectively.
As seen in the above mentioned prior art, some attempts on the development of PbMo.sub.6 S.sub.8 type compound superconductors have been done, wherein a wire material was produced by charging a mixed powder comprising respective powder constituent of PbMo.sub.6 S.sub.8, for example Mo, Pb, MoS etc. into a Ta or Mo tube subject to thermal treatment after processing, to then obtain a PbMo.sub.6 S.sub.8 compound.
Nevertheless in such attempts, a problem in the process for producing PbMo.sub.6 S.sub.8 still remains, that is, high critical current density under application of a magnetic field (Jc) could not be obtained by the prior art, since a layer of compound excellent in stoichiometric composition could not be expected from the prior art.
Then, in order to improve the Jc characteristics by densifing the powder materials, a sintering process of mixed powder by a hot press has been devised, however an applicable long wire material as a coil winding material for superconductive magnet could not be produced while only a bulk shape sized sample is obtained.